Field of the Invention
The present disclosure relates to communication buses to be used in a hazard management system. More specifically, the present disclosure relates to a hazard management system that uses one communications bus that focuses on reliability and another bus for transmission of large amounts of data.
Hazard management systems for applications such as smoke detection, intrusion detection, or water alarm are typically made up of a plurality of safety and security units. Safety units typically comprise smoke detectors, heat detectors, and flame detectors. Intrusion detectors, motion detectors, and door contacts are typical examples of security devices. Hazard management systems may also comprise at least one central unit for configuration and for monitoring individual safety and security units. A central unit is sometimes also referred to as a panel or as a management station. European published patent application EP 1 398 746 A1 describes a hazard management system with a detection unit and with a central unit. The central unit allows for an operator to change the settings of the safety and security units. A hazard management system may further provide an output unit such as a siren or a beacon. The commonly assigned European published patent application EP 2 568 457 A1 describes a hazard management system with an output unit that may activate an alarm. Combined forms of these units are also common. That is, a central unit may provide a siren and/or a detector.
The units of a hazard management system may be battery-powered. Especially in industrial environments the units would typically be connected to an external AC supply. The supply may also be backed up by an uninterruptible power supply (UPS).
Especially in industrial applications the individual detector units, the central unit and the output unit may be connected through a communications link. The communications link between the components of the hazard management system is hereafter referred to as a bus. The communications bus may be hard-wired or wireless or both. The above-noted publication EP 2 568 457 A1 discloses a radio-operated bus to connect a plurality of units.
The above-mentioned publication EP 1 398 746 A1 describes a combination of a hard-wired and of an optical link. The hard-wired link comprises resonant circuits 9, 10 that suppress noise while at the same time limiting the bandwidth of the bus.
The above-noted publication European published patent application EP 2 568 457 A1 also discloses how two input 14 and output units 16 of a hazard management system can be coupled through a communications module 20. The communication modules 20 of EP 2 568 457 A1 send and receive data to be processed by logical 26 or functional 32 modules. The link according to EP 2 568 457 A1 is wireless, nonetheless hard-wired links are typically implemented in a similar way.
Communications buses between the units of a hazard management system typically provide either reliability or large bandwidth, usually not both. Communications buses that focus on reliability are crucial in safety-relevant application where a hazard management system has to ensure an alarm is generated. They will hereafter be referred to as field buses. The very nature of a hazard management system necessitates an accurate, prompt, and reliable response in case of a fire or an intrusion into a building. Especially hazardous environments may require individual units to communicate via a fiber optic field bus in order to deal with the problem of electromagnetic interference.
It is often desirable for a hazard management system to provide units with firmware updates while these remain in service. In order to ensure the system remains responsive, a firmware update must not impair a field bus. The field bus may otherwise be fully loaded with a firmware update and not transfer safety-relevant information. Consequently, the hazard management system would no longer provide a prompt response.
Also, there may be a need for an operator to obtain additional information from a video camera built into a unit. An operator may, for instance, want to observe whether and where there is fire in a place where a fire alarm has gone off. In this case, a detector unit would provide a camera. The detector unit would then stream a video to an operator's computer in a control room. Similarly, an operator may want to verify a break-in in case an intrusion hazard management system has activated an alarm. Further, there may be a need for an operator to warn people by live voice messages.